The present invention relates to a process for separating 2,6-diisopropylnaphthalene from other isopropylnaphthalene isomers. The 2,6-diisopropyl isomer of naphthalene is of keen interest for the production of certain disubstituted aromatics which, in turn, are employed in the synthesis of liquid crystal polymers and specialty polyesters.
Such liquid crystal polymers and specialty polyesters would appear commercially attractive if either 2,6-dihydroxynaphthalene or 2,6-dicarboxynaphthalene were readily available. Unfortunately, these materials are not commercially produced because cheap, feed stocks do not exist. A viable feed stock which is convertible into either the dihydroxy or dicarboxy monomers, based upon known technology, is 2,6-diisopropylnaphthalene.
In any manufacture of diisopropylnaphthalene, it is clear that some monoisopropyl- and triisopropyl-products and a mix of diisopropyl isomers will also be obtained. In any crude diisopropylnaphthalene product which is not particularly enriched in the 2,6-diisopropylnaphthalene isomer, isomer separation by thermal distillation is very inefficient and difficult because the boiling points of 2,6-diisopropylnaphthalene and 2,7-diisopropylnaphthalene are very close. Similarly, 2,6-diisopropylnaphthalene separation by fractional crystallization using melting points is inefficient and suffers from yield problems because of the loss of the desired product in the mother liquor, and because of large recycled streams.
It is taught in U.K. patent application No. 2,199,590, filed on Nov. 27, 1987, that a specific isomer of dimethylnaphthalene can be separated from other isomers when a zeolite Y containing specific metallic ions is used as an adsorbant in combination with a specific desorbant. However, the adsorbant taught for use in the separation of the particular dimethylnaphthalene of the British reference would be of little value in isolating 2,6-diisopropylnaphthalene from other diisopropylnaphthalene isomers, since diisopropylnaphthalenes are larger molecules than dimethylnaphthalenes.
It is thus an object of the present invention to provide a selective adsorbant which has proven to be efficient in the selective adsorption of 2,6-diisopropylnaphthalene from a mixture of diisopropylnaphthalene compounds.
It is a further object of the invention to provide a process for enriching the fraction of 2,6-diisopropylnaphthalene contained in a feed stream of mixed dialkylated naphthalenes without engaging costly and inefficient distillation and crystallization techniques of the prior art.
It is still a further object of the present invention to provide a process for recovering substantially pure 2,6-diisopropylnaphthalene from a mixture of diisopropylnaphthalene isomers using selective adsorption in combination with conventional separation techniques such as fractional crystallization or distillation.